1) Field of the Invention
The present invention relates to a process and an apparatus for continuously producing polyester type polymers such as polybutylene terephthalate and polyethylene terephthalate.
2) Related Art
Since polyethylene terephthalate (hereinafter referred to as PBT) resins are excellent in the crystallizing characteristic and also excellent in mechanical properties, electric characteristics and heat resistance, they have been used for applications such as electric machines, electronic parts, mechanical parts and automobiles and their demand has been increased steadily.
Heretofore, for the general PBT production process, a terephthalic acid alkyl ester comprising dimethyl terephthalate as a main ingredient and a glycol comprising 1,4-butanediol (hereinafter referred to as BD) as a main ingredient are placed at an appropriate ratio in a mixing vessel, a transesterification catalyst is added and conditioned and then they are sent to a transesterfication reaction vessel set to a predetermined reaction temperature by a pump. In the transesterification reaction, two or three stirring vessels with stirring blades are disposed in series and methanol formed as reaction by-products, and tetrahydrofuran (hereinafter referred to as THF) formed by decomposition of the methanol formed as reaction by-products and BD and water are separated in a distillation tower. Then, a polymerization catalyst is added and the process proceeds to the polymerizing reaction step. At first, vertical stirring vessels or horizontal stirring vessels are disposed in plurality for the prepolymerization step and, further, a horizontal stirring vessel is disposed as a final polymerization step.
For continuous polycondensation process for polyethylene terephthalate, etc. in a relatively low viscosity range, operated under subatmospheric pressure, a plurality multi-tray type, columnar reactors or a plurality of vertical complete mixing type stirring vessels are used in series as disclosed in JP-A-48-7090. Oligomers of low polymerization degrees formed by esterification reaction or transesterification reaction are continuously fed to one end of such reactors to successively proceed the polycondensation reaction down to the downstream tray or while transferring the oligomers from one stirring vessel to another.
In this connection, the present inventors proposed an apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient, thereby producing an oligomer with an average degree of polymerization of 2.2 to 5, a second reactor for polycondensating the oligomer from the first reactor, thereby preparing a low polymerization product with an average degree of polymerization of 25 to 40, and a third reactor for further polycondensating the low polymerization product from the second reactor, thereby producing a high molecular weight polyester with an average degree of polymerization of 70 to 130, or further a fourth reactor for further polycondensing the polyester from the third reactor to an average degree of polymerization of 150 to 200, thereby producing a high molecular weight polyester with good heat stability and excellent hydrolysis resistance, reactors without any stirrers by an external power source being used for the first and second reactors (U.S. patent application Ser. No. 09/642587), parts of which are incorporated herein by reference.
In the apparatus, the second reactor is an approximately cylindrical vessel type, flow reactor in a double cylinder structure having an inner cylinder opening in the vessel and an inlet for the process solution at the lower part of the double cylinder structure, the process solution passing through tubes of a shell and tube type heat exchanger provided on the outside of the inner cylinder of the double cylinder structure and thereby heated to a predetermined temperature and passed upwardly to the level of the inner cylinder opening and then flowing down through the inner cylinder while the process solution is stirred with a plurality of doughnut-type trays provided on the inside wall of the outer cylinder, and the vessel is provided with an outlet for volatile matters and reaction by-products at the upper part thereof. The present inventors have found that short pass and thermal decomposition reaction of the process solution admit of improvement.
An object of the present invention is to provide an apparatus and a method for producing polybutylene terephthalate of good quality efficiently and continuously by providing a plurality of partitioned reaction compartments in the second reactor, each of the reaction compartments being stirred and heated to attain complete mixing, thereby eliminating short pass and thermal decomposition reaction of the process solution.
The object of the present invention can be attained by using, for the second reactor, a vertical cylindrical polymerization vessel having a plurality of concentrical partitioned reaction compartments therein, each of the reaction compartments being provided with stirring blades and a heater, and an outlet for volalite matters being provided at the upper part of the vessel, where polycondensation reaction is efficiently carried out, while the process solution to be treated in the reaction compartments is successively transferred radially and inwardly from the outer reaction compartment to the inner one, whereby preventing occurrence of thermal decomposition reaction and degradation of product quality.
(1) An apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient, thereby producing an oligomer with an average degree of polymerization of 2 to 5; a second reactor for polycondensating the oligomer from the first reactor, thereby preparing a low polymerization product with a low degree of polymerization; and a third reactor for further polycondensating the low polymerization product from the second reactor, thereby producing a high molecular weight polyester with an average degree polymerization of 70 to 180, or an apparatus for continuously producing polybutylene terephthalate, which comprises a first reactor for reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient, thereby producing an oligomer with an average degree of polymerization of 2 to 5, a second reactor for polycondensating the oligomer from the first reactor, thereby preparing a low polymerization product with a low degree of polymerization; a third reactor for further polycondensating the low polymerization product from the second reactor, thereby producing a high molecular weight polyester with an average degree polymerization of 70 to 130; and a fourth reactor for further polycondensing the polyester from the third reactor to an average degree of polymerization of 150 to 200, thereby producing a high molecular weight polyester, characterized in that (i) the first reactor is an approximately cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts, respectively, of the vessel proper and an outlet for volatile matters and reaction by-products at the upper part of the vessel proper, and having a calandria type heat exchanger formed in the longitudinal direction of the vessel proper and near the inside wall of the vessel proper and being immersed in the process solution, the process solution supplied into the vessel proper at the inlet at the lower part thereof is heated to a predetermined reaction temperature by the heat exchanger and is stirred and mixed by spontaneous convection due to a density difference caused by a temperature difference between the formed volatile by-product gas and the process solution, (ii) the second reactor is a vertical cylindrical polymerization vessel having a plurality of concentrated partitioned reaction compartments therein, each of the reaction compartments being provided with stirring blades and a heater, and an outlet for volatile matters being provided at the upper part of the vessel, (iii) the third reactor is a horizontal cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts on one end and an another end in the longitudinal direction of the vessel proper, respectively, and an outlet for volatile matters at the upper part of the vessel proper, and a stirring rotor rotating in the proximity of the inside wall of the vessel proper is provided in the longitudinal direction of the vessel proper, the stirring rotor in the vessel proper is provided with a plurality of stirring blade blocks in accordance with the viscosity of the process solution and the stirring blades are without any rotating shaft along the center of the stirring rotor, and (iv) the fourth reactor is a horizontal, approximately cylindrical vessel type reactor having an inlet and an outlet for a process solution at lower parts an one end and an another end in the longitudinal direction of the vessel proper, respectively, and an outlet for volatile matters at the upper part of the vessel proper, the reactor has two stirring rotors rotating in the proximity of the inside wall of the vessel proper in the longitudinal direction of the vessel proper, and the rotors each have stirring blades.
In the second reactor, each of the stirring blades can be fixed to one common half-length rotating shaft.
The second reactor can be a vertical cylindrical polymerization vessel having two partitioned concentrical reaction compartments therein each of reaction compartments being provided with stirring blades and a heating coil, the stirring blades being fixed to one common half-length rotating shaft connected to a driving means mounted on the upper part of the vessel proper, and an outlet for volatile matters being provided at the upper part of the vessel, or can be a vertical cylindrical polymerization vessel having two partitioned concentrical reaction compartments therein, the stirring blades provided in the inner reaction compartment is without any counterpart rotating shaft along the rotation center.
The term xe2x80x9cone common, half-length rotating shaftxe2x80x9d herein used means a common rotating shaft whose lower end locates above the central reaction compartment without extending into the central reaction compartment. In other words, the stirring blades in the central reaction compartment are without any counterpart rotating shaft therein. Typical embodiments of the present invention are summarized below.
(2) A process for continuously producing polybutylene terephthalate, which comprises producing an oligomer with an average degree of polymerization of 2 to 5 by reaction of an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient and then polycondensing the oligomer in series of a plurality of reactors, thereby producing a polymer of a low degree of polymerization and a high molecular weight polyester, characterized in that production of polymer of a low degree of polymerization by polycondensation of the oligomer is carried out in a vertical cylindrical polymerization vessel (initial polymerization vessel) containing a plurality of partitioned concentrical reaction compartments therein, each of the reaction compartments being. provided with stirring blades and a heater, and an outlet for volatile matters being provided at the upper part of the vessel, the polycondensation reaction can be efficiently carried out, while a process solution (oligomer) to be treated in the reaction compartments is successively transferred radially and inwardly from the outer reaction compartment to the inner one, and more specifically, a process for continuously producing polybutylene terephthalate, which comprises a first step of reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient in a first reactor, thereby producing an oligomer with an average degree of polymerization of 2 to 5, a second step of polycondensing the oligomer from the first step in a second reactor, thereby preparing a low polymerization product with an average degree of polymerization of 20 to 70, a third step of further polycondensing the low polymerization product from the second step in a third reactor, thereby producing a high molecular weight polyester with an average degree of polymerization of 70 to 180, or a process for continuously producing polybutylene terephthalate, which comprises a first step of reacting an aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof with a glycol comprising 1,4-butanediol as a main ingredient in a first reactor, thereby producing an oligomer with an average degree of polymerization of 2 to 5, a second step of polycondensing the oligomer from the first step in a second reactor, thereby preparing a low polymerization product with an average degree of polymerization of 20 to 70, a third step of further polycondensing the low polymerization product from the second step in a third reactor, thereby producing a high molecular weight polyester with an average degree of polymerization of 70 to 130, and a fourth step of further polycondensing the polyester from the third step in a fourth reactor, thereby producing a high molecular weight polyester with an average degree of polymerization of 150 to 200, characterized in that reactors characterized by (i), (ii), (iii), and (iv) described in the foregoing (1) are used; the aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof and the glycol comprising 1,4-butanediol as a main ingredient are supplied to the first step in a molar ratio of the former to the latter of 1:1.7 to 1:3.0, and the first step is carried out at 220xc2x0-250xc2x0 C. and 33 kPa-150 kPa, the second step at 230xc2x0-255xc2x0 C. and 0.5 kPa-20 kPa and the third and fourth step each at 230xc2x0-255xc2x0 C. and 0.665 kPa-0.067 kPa; the stirring blades of the second reactor is rotated in a range of 5 ppm-100 ppm; the stirring blades of the third and fourth reactors are rotated in a range of 0.5 rpm-10 rpm; total reaction time for the first to the third steps is in a range of 4-7.5 hours, or total reaction time for the first to the fourth step is in a range of 6 to 8.5 hours; a slurry of the aromatic dicarboxylic acid comprising terephthalic acid as a main ingredient or a derivative thereof and the glycol comprising 1,4-butanediol as a main ingredient prepared in a ratio of the former to the latter of 1:1.7 to 1:3.0 is supplied to the first step upon admixture of an esterifying catalyst or a polymerization reaction catalyst; and another third reactor or a plurality of third reactors is provided in parallel to the third reactor in the third step, thereby producing different kinds of polybutylene phthalate with different degrees of polymerization from that produced in the main line of the third and fourth reactors or adjusting operating conditions of each of a plurality of the third reactors to increase kinds, precise quality control and production rate of polybutylene terephthalate.